Non-rotational constant film thickness,complete step coverage evaporation system

ABSTRACT

A HIGH VACUUM METAL EVAPORATION DEPOSITION SYSTEM IS DESCRIBED WHICH AVOIDS THE NECESSITY FOR ROTATING THE TARGETS IN ORDER TO ACHIEVE AN EVEN DEPOSITION THICKNESS DISTRIBUTION OVER THE TARGET AREA.

March 5, 1974 s. PLATTER 3,795,536-

NON-ROTATIONAL CONSTANT FILM IHICKNESS, COMPLETE STEP COVERAGE EVAPORATION SYSTEM Filed Oct. 26, 1971 INVENTOR. SANDFORD PLATTER BYM/LLM Wham.

ATTORNEYS United States Patnt O 3,795,536 NON-ROTATIONAL CONSTANT FILM THICKNESS, COMPLETE STEP COVERAGE EVAPORATION SYSTEM Sanford Platter, Phoenix, Ariz., assignor to Steatite Research Corporation, Phoenix, Ariz. Filed Oct. 26, 1971, Ser. No. 192,272 Int. Cl. C23c 13/12 US. Cl. 117106 R 4 Claims ABSTRACT OF THE DISCLOSURE A high vacuum metal evaporation deposition system is described which avoids the necessity for rotating the targets in order to achieve an even deposition thickness distribution over the target area.

FIELD OF THE INVENTION This invention relates to high vacuum metal evaporation deposition systems and more particularly to improvements therein.

In a typical high vacuum metal evaporation deposition system, in order to avoid uneven film thickness distribution over the target area due to the uneven distribution of flux from the metal source in space, the target area is usually rotated about some axis perpendicular to the source. The targets are usually mounted on a special dome. However, because of the thickness of the masks which are used over the targets, because of steps in the surface of the target and because of the fact that the angle of flux striking the target varies throughout the dome, there is a shift in the pattern on the target as a result of which some of the sides of the steps in the target do not get a constant film thickness. In order to have a good step coverage, the present evaporation deposition systems provide for a planetary rotation of the targets.

The problem presented by the requirement for rotating the target is its cost of such a system. There is some vibration of critical targets as they are rotated resulting in uneven deposition. Also, wear and dirt is caused by the rotation mechanism. Some other lesser problems are, downtime due to rotation mechanism failure, targets may fall out of their holders as a result of vibration, etc.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to provide a high vacuum metal evaporation deposition system that gives a constant film thickness and good step coverage without using target rotation.

Still another object of this invention is to provide a high vacuum metal evaporation deposition system that is cheaper and less trouble-free than the systems requiring target rotation.

These and other objects of the invention are achieved in an arrangement where all targets are located on one surface of a sphere and the evaporation source or sources are located on an opposite surface of the same sphere subtending at least the same spherical area as is subtended by the targets.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of an embodiment of the invention.

FIG. 2 and FIG. 3, which are cross-sections along the lines 33 of FIG. 2 illustrate how a filamentary type of 3,795,536 Patented Mar. 5, 1974 "ice DESCRIPTION OF THE PREFERRED EMBODIMENTS In pure theory a point evaporation source located at the center of a sphere on the surface of which the targets are mounted will give uniform film thickness and normal angle. However, point sources cannot be realistically achieved. Also, the rate of evaporation from a point source is low. 7

Referring to FIG. 1 there may be seen a schematic representation of a high vacuum metal evaporation source in accordance with this invention. The high vacuum container 10 encloses a target 12 and an emitter 14 or source. The target 12 consists of one or more targets upon which it is desired to evaporate metal or other material from the source 14. The target 12 is arranged over the surface of a sphere. The angle subtended by the arrangement of the targets is represented as cu In accordance with this invention the emitting material or source 14 is arranged over the opposite surface of the same sphere and also subtends an angle a where a =a With the arrangement shown, the film thickness is constant for all targets, there is no pattern shift and there is good step coverage. The targets need not be rotated.

If the evaporation source is effectively only a fiat surface source such as a boat or a long coil filament and it and the targets are located on opposite surfaces of the same sphere, there could be a constant flux at all the targets and hence constant film thickness. However, there will still be a very poor target step coverage. In order to insure excellent step coverage it is necessary, as is shown by this invention, that the source subtend from the sphere at least the same angle as is subtended by the target, and that the source and targets occupy opposite surfaces of the same sphere.

FIG. 2 shows an arrangement for using a filamentary deposition material source. The tar-get 12 is opposite to the filamentary source 16. FIG. 3 is a view along the lines 3-3 and shows that the filamentary source comprises at least three coil filaments which are located on cords of the sphere 360 apart, where N is the number of coils and they extend from :0 to i /2 a The filamentary coils are designated as 16A, 16B, and 16C in FIG. 3.

FIG. 4 and FIG. 5 show an arrangement for flat boat sources containing the deposition material. A fiat boat is merely a flat container for the desired material to be deposited on the targets. In FIG. 4, the targets again are designated by the reference numeral 12. As may be better seen in FIG. 5, the flat boats sources 20, which are made with a large length to width ratio, are located on chords of the sphere. These sources form annulars and from FIGS. 4 and 5, it may be seen that they go from 04 :0 to /2 a If arranged in that manner, they meet the conditions for providing uniform coverage as well as step coverage of all targets.

The techniques for heating the sources are well known, therefore need not be described here.

There has accordingly been described hereinabove a novel, useful, evaporation system for use in high vacuum metal evaporation desposition systems.

What is claimed is:

1. In a high vacuum metal deposition system of the type wherein within a high vacuum container the target or targets are distributed over an area of the inside surdistributing material to be evaporated over said target at or adjacent to the inside surface of said imaginary sphere over an area which is opposite and substantially equal to the inside surface over which said targets are distributed to cover an area which subteuds the same angle as is subtended by the area of the surface overwhich said targets are distributed, and v v evaporating said material to cause an even deposition thereof on said target.

2. In high vacuum metal evaporation deposition system of the type wherein, within a vacuum container, targets are distributed over an area of the inside surface of an imiginary sphere, the improvement comprising:

sources of material to be evaporated on said targets,

and means for holding said sources-of material distributed at or adjacent to the inside surface of "said imaginary sphere over an area which is opposite and substantial- 1y equal to the area over which said targets are dis-' 'of which is, on a chord of 's'aid sphere, said 'coil'fil'amerits being spaced 36 0/N apart Where N isthe number of coils, and each of said chords along which a coiled filament extends extending from the midpoint of the area of the inside surface of said sphere subtended by said source. 4. Apparatusas recited in claim 2 wherein saidsource comprises a plurality-of boat sources each of which is on a chord of said sphere 360/N apart, where N is the number of boats, and where each of said chords extends from the center of the surface of said sphere opposite to the area of the inside surface subtended by said targets.

References Cited UNITED STATES PATENTS 3,015,586 1/1962 Toohig et al. 117-10 6 2,916,394 12/ 1959 Rychle'wski 117-106 3,507,248 4/ 1970 Seeley et a1. 117106 3,716,424 2/1973 Schoolar 117- 107 ALFRED L. LEAVI'IT, Primary Eiraminer J. W. MASSI'E, Assistant Examiner US. Cl. X.R. 118-48 

